It seems that most of us just “hack” a way around this KiCad limitation without giving much thought to how much it would change the experience for all users for much the better.
I’ve never seen any good reasons in the wishlist/bug reports that this would be overwhelming to undertake.
The question asked in the post you follow up is not automatically resolved by multi page options. The described problem is the fault of a missing feature in copy/paste. (Copy paste could offer options if it should reset references or not. Similar to how word processors ask if they should copy text only, text plus formatting, …)
The main usecase that can not be served right now is having multiple pages on any hierarchical level with local labels being confined to all these pages that are in the same level. I suspect this will the thing that will be implemented not some hack that means one has to choose between hierarchical or flat design.
This is not currently on the work plan for v6. That doesn’t mean that someone won’t take it on and submit a valid method for achieving it. But it needs to wait for the new schematic file format and then have a valid proposal that fits in long-term maintaining plans.
If this were the only feature for v6, it would not be overwhelming. But it is simply a matter of priorities right now. As @Rene_Poschl says, there is a decent work-around for flat-designs, so it doesn’t generally jump in front of issues that have no work arounds.